Lightning Spellblade question

If hypothetically I wanted to make a lightning based spellblade character, and wanted to flip Flame Reave to Lightning would Sunwreath even work, and what weapon would I look for to optimise damage?

Yes Sunwreath would still work, it’s just that the skill’s base damage (usually 2) plus any un-typed melee damage (ie, +X melee damage as contrasted with the +14 fire melee damage the ring gives) would scale with both % lightning and % fire.

Maybe whetstone gavel with a nice exalted sword for the offhand.

It increases the base damage from the off-hand weapon and any affixes. Those modifiers should be element-agnostic, e.g. Melee crit chance, melee attack speed, crit multi, increased elemental damage.

The whetstone gavel gives +2 to Flame Reave with the lightning conversion, and it has some good defensive values.